نشریه مهندسی مکانیک مدرس
سال بیستم شماره 12 (آذر 1399)

An experimental study on the critical buckling load of aluminum columns reinforced with glass/epoxy composite belts containing carbon nanotubes (CNTs) are presented in this paper. The columns with solid circular cross section are subjected to axially pressure load. Aluminum column specimens reinforced with glass/epoxy and CNT/glass/epoxy are fabricated. CNTs with 0.25, 0.5 and 1 weight percent (wt.%) are dispersed into the epoxy resin. Three layers composite belts are wrapped around the column. Glass fibers are placed along the column axes in each layer. The columns are tested under fix ended boundary conditions utilizing Instron hydraulic universal testing machine. Pressure load with respect to the end shortening are plotted for each specimen. To achieve the average value of critical buckling load, four specimen is examined for each composite belt material.  Results show that when 0.5%CNT/glass/epoxy composite belt is used to reinforce the column, the critical buckling load of the column increases by 45% with respect to the column with glass/epoxy composite belt. The proper dispersion of CNTs into the matrix material along with appropriate adhesion between the nanocomposite belt and the aluminum column lead to the increase of buckling load. Furthermore, to validate the results, buckling analysis of aluminum column reinforced with glass/epoxy composite belt was done in Abaqus finite element software. Finite element simulation confirms the experimental results obtained.

In this study, the hot-working behavior of Mn-25Ni-5Cr alloy was studied using hot compression tests at the temperatures of 850 ˚C, 900 ˚C, 950 ˚C and 1000 ˚C and the strain rates of 0.001 s-1, 0.01 s-1, 0.1 s-1 and 1 s-1 to a true strain level of 0.7. The results of flow curves showed that the flow stress decreases with increasing temperature and decreasing strain rate. Regarding the shape of flow curves, peak appearance represents the dynamic recrystallization. The peak stress and strain of flow curves appeared in fewer strains at high temperatures and strain rates. The microstructural evolution is mainly controlled by dynamic recrystallization. The presence of evolving boundaries around the recrystallized grains also indicates the occurrence of continuous dynamic recrystallization during hot working. In closer scrutiny of microstructure and fasciology, using by SEM microscope equipped with EDS detector, in addition to the background phase, second phase consisting of manganese, nickel and chromium was identified. The constants of n, α and β were determined using constitutive, power and exponential equations at 0.3 strain. According to the constitutive equation of the hyperbolic sinus, the amount of activation energy in the strain of 0.3 is 394.6258 kJ/mol.

In this paper, the experimental study of partially premixed combustion of methane and oxygen in a 5 mm mesoscale quartz reactor with 1 mm wall thickness and 5, 10, and 15 cm lengths. The partially premixed for 25%, 50%, and 75% mixing ratios paid. Experimental results including the factor of affecting flame regimes, formation range, flame dynamics, the outer wall temperature distribution of the reactor had been analyzing and reporting. The above tests were performing in an asymmetrically centered cylinder combustion chamber and a laminar flow regime. In most partial pre-mixing combustion experiments, the oscillation regime, which had an optimal heat distribution throughout the reactor, had been observed. The flame dynamics were more effect by changes in mixing ratio, reactor length, oxygen flow rate, and finally fuel flow rate (equivalence ratio). Also observed that by increasing the reactor length due to the appropriate time for homogenization of the mixture, differences in the flame formation interval were reducing in the different ratios of the pre-mixes.

Diagnosis of cell properties to isolate healthy and damaged tissues of biological cells, moving and manipulating cells and various micro/nanoparticles, imaging and diagnosis the shape of cells and different surfaces are new applications of atomic force microscopes that today use atomic force microscopes. In modeling the manipulation of micro/nanoparticles, using atomic force microscopy, one of the important points is to use a suitable and accurate contact model. Since in three-dimensional manipulation, the micro/nanoparticle is located between the beam and the substrate, contact theories must be divided into two parts. The first part is the contact between the base plate and the micro/nanoparticle and the other part is the contact between the micro/nanoparticle and the tip of the beam tip. In this study, the modulus of elasticity of gastric cancer tissue was extracted using atomic force microscopy to diagnose tissue. For this purpose, two Hertz and JKR contact models have been developed to derive the modulus of elasticity. In an experimental experiment, after isolating the cells from the gastric cancer tissue, the specimens were tested using a rectangular beam and pyramidal and spherical tips under an atomic force microscope, and the load-indentation depth diagrams were obtained. Data analysis was performed. According to the results obtained from the load-indentation depth diagram, the apparent spring coefficient for the cell can be modeled because the slope of this diagram is linear. The modulus of elasticity of the desired texture, according to the obtained diagrams obtained from the comparison of the experimental results extracted from the atomic force microscope and the results of the Hertz and JKRcontact theory of 325 ± 255 kPa, has been obtained.

The purpose of this paper is to experimentally investigate the natural frequencies of notched homogeneous and inhomogeneous specimen made from API X65 steel. The specimens cut from spiral welded pipe, tested on an equipped low blow drop weight tester with accelerometer. The tests were performed according to the API 5L standard. The homogeneous specimen was seamless and included only the base metal, while the inhomogeneous specimen included the weld seam and three zones of base metal, heat affected zone and weld. In the present study the specimens were subjected to hammer low blow in the middle without plastic deformation. The laboratory data (voltage-time) were transferred from time to frequency domain using Fourier transformation and the imposed oscillations were removed from the frequency signal by the Butterworth low pass filter. As the hammer drop height increased, the natural frequency in the specimens was almost constant. The natural frequency in the inhomogeneous specimen was less than the homogeneous specimen. Having information about the natural frequency, it is possible to prevent the destructive phenomenon of resonance in the main test (complete fracture of the specimen). Also, using the results of equipped low blow drop weight test and knowing the natural frequency, the dynamic stress intensity factor of the test specimen can be determined.

In this study, the energy absorption capacity of kevlar/elastomer composites under highspeed impact loading has been investigated experimentally and numerically. The compliance of the mechanical behavior of elastomeric composites with the theory of hyperelasticity complicates the analytical study. Therefore, numerical simulation due to the different and complex mechanisms of failure has gained large share in the design of composite structures. In the present study, the most advanced method of finite element modeling of composites i.e., Abaqus / Explicit has been used to determine their behavior during impact. For this purpose, planer shell elements were used to model the composite layers, and formable material model and the vumat were used to determine the behavior of the elastomeric composite failure model based on a damage criterion such as von mises failure criterion. Due to the lack aforementioned criteria in the commercial versions of the software and the importance of considering damages in numerical simulation for these composites, the criterion was written in Fortran software environment, and the analysis of the penetration phenomenon was added to the software capability in composite structure. In order to validate this model, an experimental test was performed on the kevlar/elastomer composite by a Gas gun device. Also, the study of deformation, output projectile velocity, and absorpted energy have been reported. The simulation results show a very good agreement with the experimental results.